Secondary-battery monitoring device and prediction method of battery capacity of secondary battery

Abstract

A secondary-battery monitoring device includes: a use-state memory device that stores a transition of a load parameter indicating a use state of a secondary battery; and a battery capacity prediction device that predicts a temporal change of a battery capacity of the secondary battery on the basis of a prediction function. The prediction function is derived from a relation between growth of a film formed in an electrode surface of the secondary battery and a reduction of a precursor component of the film which is contained in an electrolyte of the secondary battery. The battery capacity prediction device determines a coefficient of the prediction function on the basis of the transition of the load parameter which is stored in the use-state memory device, and predicts the temporal change of the battery capacity of the secondary battery on the basis of the prediction function which uses the coefficient.

The invention claimed is: 
     
       1. A secondary-battery monitoring device that improves accuracy of measuring deterioration in a secondary-battery, comprising:
 a sensor that detects a temperature of the secondary-battery; 
 a memory that stores a transition of a load parameter indicating a use state of a secondary battery; and 
 a processor that is communicatively coupled with the sensor and the memory, wherein the processor is configured to: 
 perform a first life test on the secondary battery to determine a capacity of the secondary battery over a plurality of time intervals for a plurality of test conditions for which load parameters are varied, 
 generate a plot of the capacity of the secondary battery for the plurality of test conditions, wherein the plot combines the capacity of each of the load parameters determined for the plurality of time intervals, 
 determines a coefficient A by fitting a first curve to the plot, wherein the coefficient A is fit so that the coefficient A is independent of the load parameters, 
 determines coefficients τ by fitting a second curve to the plot for each of the load parameters, wherein the coefficients τ are dependent on the load parameters, 
 stores the coefficient A and the coefficients τ in the memory, 
 receive the temperature of the battery from the sensor, and 
 predict, using a prediction function, a temporal change of a battery capacity of the secondary battery based on the temperature of the battery received form the sensor and the coefficient A and the coefficients τ stored in the memory, 
 wherein the prediction function is a function derived from a relation between a growth of a film which is formed in an electrode surface of the secondary battery, and a reduction of a precursor component of the film which is contained in an electrolyte of the secondary battery, and 
 wherein the prediction function is expressed as follows:
     Q ( t )= Q   max,ini   −Q   max,ini   *X ( t ); 
 
 where Q(t) is a predicted battery capacity of the secondary battery, Q max,ini  is an initial capacity of the secondary battery and X(t) satisfies: 
 
       
         
           
             
               
                 t 
                 τ 
               
               = 
               
                 
                   - 
                   
                     ln 
                     ⁡ 
                     
                       ( 
                       
                         1 
                         - 
                         
                           
                             X 
                             ⁡ 
                             
                               ( 
                               t 
                               ) 
                             
                           
                           A 
                         
                       
                       ) 
                     
                   
                 
                 - 
                 
                   
                     X 
                     ⁡ 
                     
                       ( 
                       t 
                       ) 
                     
                   
                   A 
                 
               
             
           
         
         where a particular value of τ is retrieved from the memory based on the temperature of the battery received from the sensor. 
       
     
     
       2. The secondary-battery monitoring device according to  claim 1 ,
 wherein the load parameter includes at least one of a temperature of the secondary battery, a state of charge (SOC) of the secondary battery, a voltage of the secondary battery, and a current flowing to the secondary battery. 
 
     
     
       3. The secondary-battery monitoring device according to  claim 1 , further comprising:
 a battery capacity detection device that detects the battery capacity of the secondary battery; and 
 a counting device that counts a use time of the secondary battery, 
 wherein the memory further stores, as a transition of the load parameter, a relation between the battery capacity of the secondary battery detected by the battery capacity detection device and the use time of the secondary battery counted by the counting device. 
 
     
     
       4. A prediction method of a battery capacity of a secondary-battery that improves accuracy of measuring deterioration in the secondary-battery, comprising:
 performing, by a processor, a first life test on the secondary battery to determine a capacity of the secondary battery over a plurality of time intervals for a plurality of test conditions for which load parameters are varied; 
 generating, by the processor, a plot of the capacity of the secondary battery for the plurality of test conditions, wherein the plot combines the capacity of each of the load parameters determined for the plurality of time intervals, 
 determining, by the processor, a coefficient A by fitting a first curve to the plot, wherein the coefficient A is fit so that the coefficient A is independent of the load parameters, 
 determining, by the processor, coefficients τ by fitting a second curve to the plot for each of the load parameters, wherein the coefficients τ are dependent on the load parameters, 
 storing, by the processor, the coefficient A and the coefficients τ in a memory, 
 receiving, by the processor a temperature of the secondary-battery measured by a sensor; and 
 predicting, using a prediction function, a temporal change of a battery capacity of the secondary battery based on the temperature of the battery received form the sensor and the coefficient A and the coefficients τ stored in the memory wherein the prediction function is a function derived from a relation between a growth of a film formed in an electrode surface of the secondary battery and a reduction of a precursor of the film contained in an electrolyte of the secondary battery; 
 wherein the prediction function is expressed as follows:
     Q ( t )= Q   max,ini   −Q   max,ini   *X ( t ) 
 
 where Q(t) is a predicted battery capacity of the secondary battery, Q max,ini  is an initial capacity of the secondary battery, and X(t) satisfies: 
 
       
         
           
             
               
                 t 
                 τ 
               
               = 
               
                 
                   - 
                   
                     ln 
                     ⁡ 
                     
                       ( 
                       
                         1 
                         - 
                         
                           
                             X 
                             ⁡ 
                             
                               ( 
                               t 
                               ) 
                             
                           
                           A 
                         
                       
                       ) 
                     
                   
                 
                 - 
                 
                   
                     X 
                     ⁡ 
                     
                       ( 
                       t 
                       ) 
                     
                   
                   A 
                 
               
             
           
         
         where a particular value of τ is retrieved from the memory based on the temperature of the battery received from the sensor. 
       
     
     
       5. The prediction method of the battery capacity of the secondary battery according to  claim 4 , further comprising:
 detecting the battery capacity of the secondary battery; 
 counting a use time of the secondary battery; and 
 using a relation between the detected battery capacity of the secondary battery and the use time of the secondary battery as a transition of the load parameter.